This invention relates to a halogen-containing thermoplastic resin composition having markedly improved long-run moldability.
Halogen-containing thermoplastic resins, represented by polyvinyl chloride resin, are not only comparatively inexpensive but generally satisfactory in clarity, mechanical properties and processability so that they find application in a broad spectrum of products such as film, sheet, hose, flexible container, coated cloth, leather cloth, cover sheet, tarpaulin, shoe sole, sponge, wire covering, household goods and so on.
However, halogen-containing thermoplastic resins have the disadvantage of a narrow molding temperature range because of proximity between the processable temperature and thermal degradation temperature, not to speak of their poor service durability and low impact resistance.
In order to improve their moldability and other properties, it has been practiced to blend halogen-containing thermoplastic resins with various modifying resins such as polyethylene chloride, ethylene-vinyl acetate copolymer, acrylonitrile-butadiene-styrene terpolymer, (meth)acrylate copolymer, etc. Of these modifying resins, ethylene-vinyl acetate copolymer has been considered to be particularly useful.
The use of a grafted ethylene-vinyl acetate copolymer as a modifying resin has also been proposed and attracting attention.
For example, Japanese Patent Publication No. 30699/1979 discloses a resin composition prepared by graft-emulsion-polymerizing an olefin with an aqueous dispersion of an ethylene-vinyl acetate copolymer (ethylene content 85-60 weight %) to prepare a graft copolymer and compounding this graft copolymer and a liquid plasticizer with vinyl chloride resin.
Japanese Patent Application KOKAI No. 16949/1986 discloses a resin composition prepared by suspension-polymerizing a vinyl monomer, for example vinyl acetate, ethylene, methyl acrylate, ethyl acrylate, methyl methacrylate, acrylonitrile, etc., which has a solubility parameter of 8.5 to 15, in the presence of an emulsion-polymerized ethylene-vinyl acetate copolymer with a vinyl acetate content of 90 to 50 weight % to give a modified ethylene-vinyl acetate copolymer and, then, blending this modified copolymer with vinyl chloride resin.
Japanese Patent Application KOKAI No. 127334/1987 discloses a resin composition prepared by blending vinyl chloride resin with a butadiene-vinyl monomer (selected from the group consisting of styrenes, acrylonitriles and (meth)acrylates) copolymer and a graft copolymer prepared by treating a vinyl esterethylene copolymer with a vinyl monomer (selected from the group consisting of styrenes, acrylonitriles and (meth)acrylates) under graft-copolymerization conditions.
Furthermore, Japanese Patent Publication Nos. 22909/1969, 23027/1970 and 11704/1980 disclose methods of blending a grafted ethylene-vinyl acetate copolymer with polyvinyl chloride resin.
However, such methods for blending an ethylene-vinyl acetate copolymer with polyvinyl chloride resin have the following disadvantages.
(a) When the ethylene-vinyl acetate copolymer is a pulverizate of a solution polymerization product, its homogeneous miscibility with polyvinyl chloride is poor.
(b) When the ethylene-vinyl acetate copolymer is a suspension polymerization product, the blocking problem tends to occur if premixing is carried out en masse prior to melt-molding (extrusion molding or calendering). In other words, hot blending is difficult. Furthermore, in calendering, the plate-out problem (adhesion of the blend to the metal roll) tends to occur. In the case of extrusion molding, the melt viscosity of copolymer falls remarkably and so that the heterogeneous dispersion tends to occur.
(c) When the ethylene-vinyl acetate copolymer is an emulsion polymerization product, the heat resistance of the product is sacrificed in addition to the above-mentioned disadvantages (b).
When the resin compositions proposed in the above patent literature are actually used in the field or the graft copolymers described there are purchased from commercial sources and blended with polyvinyl chloride resin, the results are better than those achieved by blend of the ethylene-vinyl acetate copolymer but the long-run moldability is not fully satisfactory and the heat resistance and homogeneous miscibility are often inadequate.
The inventor of the present invention has found that the above-mentioned disadvantages can be overcome by blending the grafted ethylene-vinyl acetate copolymer described hereinafter with polyvinyl chloride resin. The present invention has been predicated on the above finding.